Biosensors are sensors that detect chemical species with high selectivity on the basis of molecular recognition rather than the physical properties of analytes. See, e.g., Advances in Biosensors, A. P. F. Turner, Ed. JAI Press, London, (1991). Many types of biosensing devices have been developed in recent years, including enzyme electrodes, optical immunosensors, ligand-receptor amperometers, and evanescent-wave probes.
The detection mechanism in such sensors can involve changes in properties such as conductivity, absorbance, luminescence, fluorescence and the like. Various sensors have relied upon a binding event directly between a target agent and a signaling agent to essentially turn off a property such as fluorescence and the like. The difficulties with present sensors often include the size of the signal event which can make actual detection of the signal difficult or affect the selectivity or make the sensor subject to false positive readings.
Amplification of fluorescence quenching has been reported in conjugated polymers. For example, Swager, Accounts Chem. Res., 1998, v. 31, pp. 201–207, describes an amplified quenching in a conjugated polymer compared to a small molecule repeat unit by methylviologen of 65; Zheng et al., J. Appl. Polymer Sci., 1998, v. 70, pp. 599–603, describe a Stern-Volmer quenching constant of about 1000 for poly(2-methoxy,5-(2′-ethylhexloxy)-p-phenylene-vinylene (MEH-PPV) by fullerenes; and, Russell et al., J. Am. Chem. Soc., 1982, v. 103, pp. 3219–3220, describe a Stern-Volmer quenching constant for a small molecule (stilbene) in micelles of about 2000 by methylviologen. Despite these successes, continued improvements in amplification of fluorescence quenching have been sought. Surprisingly, a Ksv of greater than 105 has now been achieved.
It is an object of the present invention to provide a specific sensing system wherein the sensor can yield a distinctly recognizable signal event upon the binding of a target agent by a recognition element of the sensor.
It is a further object of the invention to provide a chemical moiety for use in a sensor system, the chemical moiety including a recognition element, a tethering element and a property-altering element.